Method and apparatus for forming resin film

ABSTRACT

The apparatus is for forming a resin film from a resin for a middle portion to form a resin film main body of the resin film and a resin for edge portions to form both side edge portions in a crosswise direction of the resin film. The apparatus comprises: a feed block which includes a joining part where the resin for the middle portion in a molten state and the resin for the edge portions in a molten state are joined in such a manner as to enclose both side edges in the crosswise direction of the resin film main body with the resin for the edge portions; and an extruding die through which the joined resins are extruded to form the resin film. Thus, a method and apparatus for forming the resin film can avoid the inclusion of the resin for the middle portion in the trimmed-off selvages while preventing the film separation of the resins for the middle portion and for the edge portions, and therefore, increase the recyclability and the productivity of the resin film.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method and apparatus forforming a resin film, in particular, to a method and apparatus forforming a resin film in which a resin for use in the edge portion of theresin film is applied to both side edges in the crosswise direction ofthe resin film main body, which is formed of a resin for use in themiddle portion of the resin film, at the time the resins in the moltenstate are extruded through an extruding die to form the resin film.

[0003] 2. Description of the Related Art

[0004] In a resin film having been extruded through an extruding die,its selvages (both side edges in the crosswise direction of the resinfilm) are usually trimmed off in the post-processing. When the resinfilm is formed of a resin hard to recycle or poor in thermal stability,the trimmed-off selvages cannot be recycled, which leads to decrease inthe yield of the resin film. Hence, in order to make possible therecycling of resin films, there have been proposed a technique forforming a resin film in which a resin for use in the edge portion of theresin film is applied to both side edges in the crosswise direction ofthe resin film main body (the portion of the resin film left aftertrimming off its selvages and to be an end product), which is formed ofa resin for use in the middle portion of the resin film. For example,when forming the resin film main body of a resin poor in thermalstability, a resin for the edge portions excellent in thermal stabilityis applied to both side edges of the main body and then the resin forthe edge portions is trimmed off as the selvages. This allows therecycling of resin films and the improvement in productivity, becausethe trimmed-off resin for the edge portions is hard to subject to heatdeterioration even when it is used repeatedly.

[0005] However, the techniques still have disadvantages in that when thephysical properties of the resins for the middle portion and for theedge portions of a resin film are different or the film formingcondition such as applying condition is different, the resins are likelyto separate from each other or the boundary between them is likely to bein disorder. If the boundary is in disorder, the proportion of theinclusion of the resin for the middle portion to the trimmed-offselvages becomes large, which causes not only the deterioration of theresin film recyclability, but also the decrease in productivity, due tothe decrease in the portion as a resin film main body.

[0006] As a measure to prevent the occurrence of the above problems,Japanese Patent Application Publication No. 2002-240126 discloses amethod to prevent the film separation of the resin for the edge portionsand the resin for the middle portion by wrapping up the former in thelatter. However, this has the disadvantage in that, since the resin forthe edge portions is wrapped up in the resin for the middle portion, theresin for the middle portion accounts for a larger part of the resin ofthe trimmed-off selvages than the resin for the edge portions, causingthe deterioration in not only recyclability but also productivity. Inother words, in order to increase the recyclability and productivity ofresin films, it is important to arrange the resins for the edge portionsand for the middle portion in such a manner as to avoid their minglingas much as possible when trimming off the selvages of the resin film,and furthermore, it is important to make their boundary in order andtheir boundary line clear. It is necessary to avoid the film separationof the two resins while satisfying the above requirements.

[0007] Further, Japanese Patent Application Publication No. 1-64822discloses an apparatus for forming such kind of resin film, which adoptsa detachable assembly. Still further, Japanese Patent ApplicationPublication No. 7-76038 discloses an apparatus for forming such kind ofresin film, in which a resin for the edge portions of a resin film and aresin for the middle portion of the resin film are layered in thecrosswise direction in an extruding die. However, even with theseapparatuses, the problems of the film separation of the resins and thedisorder at the boundary between the resins cannot be resolved.

SUMMARY OF THE INVENTION

[0008] The present invention has been made in the light of the abovesituation. Accordingly, the object of the present invention is toprovide a method and apparatus for forming a resin film which can avoidthe inclusion of the resin for the middle portion of the resin film inthe trimmed-off selvages while preventing the film separation of theresins for the middle portion and for the edge portions, and therefore,increase the recyclability and the productivity of the resin film.

[0009] In order to attain the above-described object, the presentinvention is directed to a method of forming a resin film from a resinfor a middle portion to form a resin film main body of the resin filmand a resin for edge portions to form both side edge portions in acrosswise direction of the resin film, the method comprising the stepsof: joining the resin for the middle portion in a molten state and theresin for the edge portions in a molten state in such a manner as toenclose both side edges in the crosswise direction of the resin filmmain body with the resin for the edge portions; and extruding the joinedresins through an extruding die to form the resin film.

[0010] Joining the resins for the middle portion and for the edgeportions in such a manner as to enclose both side edges in the crosswisedirection of the resin film main body with the resin for the edgeportions. (herein after referred to as “the joining method of thepresent invention”) can reduce the disorder at the boundary between theresins for the middle portion and for the edge portion, while preventingthe film separation of the two resins. This makes it possible to avoidthe inclusion of the resin for the middle portion in the trimmed-offselvages as much as possible, which in turn increases the recyclabilityof the selvages, and hence the yield and the productivity of theproduct.

[0011] Preferably, a degree of enclosing the resin for the middleportion with the resin for the edge portions is adjusted according to adifference in Melt Flow Rate (MFR) between the resins. Generally, thelarger the difference in MFR between the resins for the middle portionand for the edge portions becomes, the more the film separation of thetwo resins is apt to occur; therefore, when the difference in MFR islarger, the degree of enclosing is required to be higher. Conversely,when the difference in MFR is small, even if the degree of enclosing islowered, the film separation does not occur between the resins.Accordingly, the degree of enclosing which reflects the difference inMFR between the resins for the middle portion and for the edge portionscan be achieved by changing the degree according to the difference inMFR between the two resins. Doing this avoids the unnecessary inclusionof the resin for the middle portion in the trimmed-off selvages, andmoreover, prevents the film separation of the two resins reliably. Inthis case, when the difference between the resins for the middle portionand for the edge portions is expressed in terms of MFR ratio, preferablythe MFR ratio is in the range of 0.5 to 2. This is because if the MFRratio is as large as more than 2, the film separation may sometimesoccur between the resins even with the joining method of the presentinvention.

[0012] The term “Melt Flow Rate (MFR)” herein used means the amount of athermoplastic resin, by gram-weight, extruded through an orifice of 2.1mm in diameter and 8 mm in length for 10 minutes when a force of 2310 g(44 pis) is applied to the resin at 230° C. (for the measuring method,refer to JIS K 7210, ASTMD 1238).

[0013] Preferably, a degree of enclosing the resin for the middleportion with the resin for the edge portions is adjusted according to adifference in extrusion rate between the resins. Generally, the largerthe difference in extrusion rate between the resin for the middle andthe resin for the edge portions becomes, the more the disorder is likelyto occur at the boundary between the resins. However, if the degree ofenclosing is increased with the increase in the difference in extrusionrate, the disorder at the boundary can be reduced. Conversely, when thedifference in extrusion rate is small, even if the degree of enclosingis lowered, the disorder does not occur at the boundary between theresins. Accordingly, the degree of enclosing which reflects thedifference in extrusion rate between the resins for the middle portionand for the edge portions can be achieved by changing the degreeaccording to the difference in extrusion rate between the two resins.Doing this avoids the unnecessary inclusion of the resin for the middleportion in the trimmed off selvages, and moreover, reduces the disorderat the boundary between the two resins reliably. In this case, when thedifference between the resins for the middle portion and for the edgeportions is expressed in terms of extrusion rate ratio, preferably theextrusion rate ratio is 0.2 or less. This is because if the extrusionrate ratio is as large as more than 0.2, not only the film separationmay sometimes occur between the resins, but also the disorder is morelikely to occur at the boundary between the resins even with the joiningmethod of the present invention. More preferably, the degree ofenclosing is changed according to the two factors: the difference inextrusion rate; and the difference in MFR.

[0014] Preferably, a degree of enclosing the resin for the middleportion with the resin for the edge portions is adjusted according to adifference in resin temperature between the resins. Generally, thelarger the difference in resin temperature between the resins for themiddle portion and for the edge portions becomes, the more the filmseparation of the two resins is apt to occur; therefore, when thedifference in resin temperature is larger, the degree of enclosing isrequired to be higher. Conversely, when the difference in resintemperature is small, even if the degree of enclosing is lowered, thefilm separation does not occur between the resins. Accordingly, thedegree of enclosing which reflects the difference in resin temperaturebetween the resins for the middle portion and for the edge portions canbe achieved by changing the degree according to the difference in resintemperature between the two resins. Doing this avoids the unnecessaryinclusion of the resin for the middle portion in the trimmed offselvages, and moreover, prevents the film separation of the two resinsreliably. In this case, when the difference between the resins for themiddle portion and for the edge portions is expressed in terms of resintemperature ratio, preferably the resin temperature ratio is in therange of 0.8 to 1.2. This is because if the resin temperature ratio isoutside the above range, not only the film separation may sometimesoccur between the resins, but also the disorder is more likely to occurat the boundary between the resins even with the joining method of thepresent invention. More preferably, the degree of enclosing is changedaccording to the three factors: the difference in resin temperature; thedifference in MFR; and the difference in amount of resin supplied.

[0015] Preferably, a degree of enclosing the resin for the middleportion with the resin for the edge portions is adjusted according to awidth of the resin film. Generally, the larger the width of the resinfilm becomes, the larger the disorder becomes at the boundary betweenthe resins. However, if the degree of enclosing is increased with theincrease in the width of the resin film, the disorder at the boundarycan be reduced. Conversely, when the width of the resin film is small,even if the degree of enclosing is not increased, the disorder does notoccur at the boundary between the resins. Accordingly, the degree ofenclosing which reflects the width of the resin film can be achieved bychanging the degree according to the width of the resin film. Doing thisavoids the unnecessary inclusion of the resin for the middle portion inthe trimmed off selvages, and moreover, reduces the disorder at theboundary between the two resins reliably. In this case, preferably thewidth of the resin film is 5 meters or less. This is because if thewidth is more than 5 meters, the disorder is more likely to occur at theboundary between the resins. More preferably, the degree of enclosing ischanged according to the four factors: the width of the resin film, thedifference in resin temperature, the difference in MFR and thedifference in extrusion rate.

[0016] In order to attain the above-described object, the presentinvention is also directed to an apparatus for forming a resin film froma resin for a middle portion to form a resin film main body of the resinfilm and a resin for edge portions to form both side edge portions in acrosswise direction of the resin film, the apparatus comprising: a feedblock which includes a joining part where the resin for the middleportion in a molten state and the resin for the edge portions in amolten state are joined in such a manner as to enclose both side edgesin the crosswise direction of the resin film main body with the resinfor the edge portions; and an extruding die through which the joinedresins are extruded to form the resin film.

[0017] According to the present invention, the disorder at the boundarybetween the resins for the middle portion and for the edge portions isdecreased while preventing the film separation of the two resins.Accordingly, it becomes possible to avoid the inclusion of the resin forthe middle portion in the trimmed off selvages as much as possible,which in turns increases the recyclability of the selvages, and hencethe yield and the productivity of the product.

[0018] Preferably, a trunk flow path through which the resin for themiddle portion flows and a pair of branch flow paths through which theresin for the edge portions flows are joined at the joining part in thefeed block; and a cross-sectional shape of the joining part is formed toallow the side edges of the resin film main body to be enclosed with theresin for the edge portions. This is a preferred example of constructionfor the feed block with which the side edges of the resin film main bodyare enclosed with the resin for the edge portions. The term“cross-sectional shape” herein used means the shape of the cross sectionperpendicular to the direction of the flow of the resins which flowthrough the joining part.

[0019] Preferably, the feed block is adapted to be detachably providedwith any one of a plurality of joining part blocks having respectivejoining parts different in degree of enclosing the side edges of theresin film main body with the resin for the edge portions; and one ofthe plurality of joining part blocks which specifies a joiningconfiguration depending on condition under which the resin film isformed is attached to the feed block exchangeably for another of theplurality of joining part blocks.

[0020] According to the present invention, since the feed block is soconstructed that any one of the joining part blocks, which specify thejoining configuration, is exchangeable for another depending on thecondition under which the resin film is formed, even if the condition,such as physical properties of the resin for the middle portion and theresin for the edge portions and the applying condition of the same ischanged, it is only necessary to exchange the joining part block for asuitable one. Thus, resin films are very conveniently formed.

[0021] Preferably, the condition under which the resin film is formedincludes at least one of a difference in MFR, an extrusion rate andresin temperature between the resin for the middle portion and the resinfor the edge portions and a width of the resin film. This allows thefeed block having the suitable joining part to be selected and useddepending on the factors which affect the film separation of the resinfor the middle portion and the resin for the edge portions and thedisorder occurring at the boundary between the two resins.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The nature of the present invention, as well as other objects andadvantages thereof, will be explained in the following with reference tothe accompanying drawings, in which like reference characters designatethe same or similar parts throughout the figures and wherein:

[0023]FIG. 1 is a general block diagram of an apparatus for forming aresin film according to an embodiment of the present invention;

[0024] FIGS. 2(a) and 2(b) are front and side elevations, respectively,illustrating an extruding die with a feed block, and FIG. 2(c) is anenlarged view illustrating a joining part;

[0025]FIG. 3 is a sectional view showing a cross-sectional shape of thejoining part of the feed block;

[0026]FIG. 4 is a cross-sectional view of a lamination resin formed bythe joining part of the feed block;

[0027]FIG. 5 is a sectional view showing another cross-sectional shapeof the joining part of the feed block;

[0028]FIG. 6 is a cross-sectional view of a lamination resin formed inComparative Example 1;

[0029]FIG. 7 is a cross-sectional view of a lamination resin formed inExample 1;

[0030]FIG. 8 is a cross-sectional view of a lamination resin formed inComparative Example 3;

[0031]FIG. 9 is a cross-sectional view of a lamination resin formed inExample 3;

[0032]FIG. 10 is a cross-sectional view of a lamination resin formed inExample 4;

[0033]FIG. 11 is a cross-sectional view of a lamination resin formed inExample 5; and

[0034]FIG. 12 is a sectional view showing one example of exchangestructure provided to the feed block main body with which one joiningpart block can be exchanged for another.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] In the following, preferred embodiments of the method andapparatus of forming a resin film in accordance with the presentinvention will be described in detail with reference to the accompanyingdrawings.

[0036]FIG. 1 is a general block diagram of an apparatus 10 for forming aresin film according to an embodiment of the present invention. Theapparatus will be described taking the case where a film-like laminate27 is formed by laminating a support 22 with a resin film 11.

[0037] As shown in FIG. 1, below an extruding die 12 with a feed block13, through which resins in the molten state are extruded so that theresin film 11 is formed, a cooling roller 14 and a nip roller 16 arearranged adjacent to and parallel with each other; in addition, on theopposite side of the nip roller 16 across the cooling roller 14, a filmdetaching roller 18 is arranged adjacent to and parallel with thecooling roller 14. The resin film 11 extruded through the extruding die12 is applied to the web-like support 22 conveyed from the upstream,runs through between the cooling roller 14 and the nip roller 16 andbetween the cooling roller 14 and the film detaching roller 18 whilekept in contact with the circumference of the cooling roller 14, and isdetached from the cooling roller 14 at the position of the filmdetaching roller 18. Thus, the film-like laminate 27 is produced. As thesubstrate 22, paper, resin or metal can be used depending on thefilm-like laminate 27 required. As the resin of which the resin film isformed, known thermoplastic resins, for example, polyolefin resins suchas polyethylene and polypropylene can be used.

[0038] FIGS. 2(a), 2(b) and 2(c) illustrate an extruding die 12 with afeed block, and FIG. 2(a) is a front elevation of the extruding die 12,FIG. 2(b) is a side elevation of the extruding die 12, and FIG. 2(c) isan enlarged view illustrating a joining part 36, respectively.

[0039] As shown in FIGS. 2(a) and 2(b), the feed block 13 is detachablyattached to the extruding die 12 by fastening each other's flange parts13A, 12A with bolts 17. In the inside of the feed block 13, a trunk flowpath 32, through which a resin A for the middle portion for forming aresin film main body 11A arranged in the middle portion of the resinfilm 11 in terms of its width direction flows, a pair of branch flowpaths 34, 34, through which a resin B for the edge portions for formingboth edge portions 11B of the resin film 11 in terms of its widthdirection flows, and a joining part 36, in which the pair of branch flowpaths 34 join the trunk flow path 32, are formed. The joining part 36 isformed so that its cross section has such a shape as a pair of recessedbranch flow paths 34 are fitted on the respective projecting edges ofthe trunk flow path 32, as shown in FIG. 3 (a cross-sectional view ofthe joining part 36 taken along the line 3-3 of FIG. 2(a)). This shapeallows the resin A for the middle portion, which flows through the trunkflow path 32, and the resin B for the edge portions, which flows throughthe pair of branch flow paths 34, to join together at the joining part36 and, as shown in FIG. 4, the resin B for the edge portions is appliedto the side edge portions of the resin film main body 11A in such amanner as to enclose the side edges of the resin film main body with theresin B. A lamination resin 15 having been formed by lamination at thejoining part 36 (refer to FIG. 4) is fed from the joining part 36 to theextruding die 12. The feed block 13 is so constructed that any one of aplurality of joining part blocks 13D having respective joining partsdifferent in degree of enclosing the resin A for the middle portion withthe resin B for the edge portions can be detachably attached thereto andany one of the joining part blocks 13D which specify the joiningconfiguration is exchangeable for another depending on the conditionunder which resin films are formed. As for the exchange structureprovided to the feed block 13 with which one joining part block 13D canbe exchanged for another, for example, a structure can be suitably usedwhich comprises a feed block main body 13B and a penetration 13C formedlaterally in the feed block main body 13B and whose penetration 13C ajoining part block 13D is inserted into or drawn out. A closure plate13E for closing one end of the penetration 13C is detachably attached tothe feed block main body 13B by, for example, bolting. The closure plate13E may be provided on both ends of the penetration 13C. A plurality ofjoining part blocks 13D having respective joining parts 36 different indegree (L) to which the resin A for the middle portion is enclosed withthe resin B for the edge portions are prepared and a joining part block13D, which specifies the joining configuration, is exchanged for a moresuitable one depending on the condition under which resin films areformed, such as difference in MFR between the resin A for the middleportion and the resin B for the edge portion, difference in extrusionrate between the resin A for the middle portion and the resin B for theedge portion, difference in resin temperature between the resin A forthe middle portion and the resin B for the edge portions and the widthof the resin film 11.

[0040] When the resin film main body 11A is made up of two layers usingtwo kinds of resins A and A′ for the middle portion, preferably thedegree (L₁) and (L₂) to which the resins A and A′ are enclosed with theresin B for the edge portions are changed as shown in FIG. 5, dependingon the physical properties of the resins and the condition under whichthe resins are applied. This is because the film separation tendency ofthe resins and the disorder at the boundary between the resins differdepending on the difference in MFR between the resins, the difference inextrusion rate between the resins, the difference in resin temperaturebetween the resins and the width of the resin film 11. The relationshipbetween the physical properties of the resins or the applying conditionand the degree (L) to which the resin A for the middle portion isenclosed with the resin B for the edge portions can be obtained byconducting tests.

[0041] As shown in FIGS. 2(a) and 2(b), the extruding die 12 comprises amanifold 28 and a slit 30, and the lamination resin 15 fed into theextruding die 12 is spread in the width direction of the extruding die12 (the width direction of the resin film 11), run through the slit 30and extruded from the extruding die 12 outside.

[0042] Then the method of forming a resin film according to anembodiment of the present invention will be described with reference tothe apparatus 10 for forming a resin film which is constructed asdescribed above.

[0043] First, as a preliminary, a joining part block 13D having asuitable joining part 36 is selected depending on the differences inMFR, extrusion rate and resin temperature between the resin A for themiddle portion and the resin B for the edge portions and the width ofthe resin film 11 and then fitted to the feed block main body 13B. Thenthe resin A for the middle portion and the resin B for the edge portionsare fed to the feed block 13. The resin A may consist essentially of asingle kind of resin to form a single layer, or may consist essentiallyof a plurality of kinds of resins to form a plurality of layers, and maycomprise at least one kind of resin to form at least one layer andinorganic pigments, additives or the like. The resin B for the edgeportions may consist essentially of at least one kind of resin, and maycomprise at least one kind of resin and additives; however, taking intoaccount the recyclability of trimmed-off selvages, the resin Bpreferably consists essentially of a single kind of resin.

[0044] The resin A for the middle portion and the resin B for the edgeportions both having been fed to the feed block 13 are joined andlayered together in the molten state at their melting points or higherat the joining part 36 and fed to the extruding die 12 as the laminationresin 15 whose middle portion is formed of the resin A for the middleportion and edge portions are formed of the resin B for the edgeportion. The lamination resin 15 having been fed into the extruding die12 is spread in the width direction of the extruding die 12 (the widthdirection of the resin film 11) in the manifold 28, run through the slit30 and extruded as the resin film 11 from the extruding die 12 outside.The resin film 11 having been extruded from the extruding die 12 isoxidized with oxidizing gases such as air and ozone so that it cansufficiently adhere to the support 22, which is conveyed from theupstream and nipped between the cooling roller 14 and the nip roller 16,and is then applied to the support 22. The resin film 11 having beenapplied to the support 22 is fully cooled with the cooling roller 14 anddetached from the cooling roller 14 with the film detaching roller 18.Thus, the film-like laminate 27 made up of the support 22 laminated withthe resin film 11 is produced. The film-like laminate 27 thus producedis made to be an end product by trimming off the selvages thereof in thepost-processing.

[0045] In the present embodiment, since the resin A for the middleportion and the resin B for the edge portions are joined together at thejoining part 36 of the feed block 13 in such a manner as to enclose bothside edges in the crosswise direction of the resin film main body 11A,which is formed of the resin A, with the resin B, the disorder occurringat the boundary between the resin A for the middle portion and the resinB for the edge portions can be reduced while preventing the filmseparation of the resins A and B constituting the resin film 11. Thismakes it possible to avoid the inclusion of the resin A for the middleportion in the trimmed off selvages as much as possible, which in turnincreases the recyclability of the selvages, and the yield and theproductivity of the product.

[0046] Further, since the feed block 13 is so constructed that any oneof a plurality of joining part blocks 13D, which have been prepareddepending on the condition under which resin films is formed, isexchangeably attached to the feed block main body 13B and any one of thejoining part blocks 13D having a suitable joining part 36 for thecondition under which the resin film 11 is formed can be used, not onlythe film separation of the resin A for the middle portion and the resinB for the edge portions can be prevented reliably, but also the disorderat the boundary between the resins can be reduced effectively. Thiscontributes to further increase in recyclability and productivity ofresin films.

[0047] While the embodiment of the present invention has been describedtaking the case of the film-like laminate 27, which is made up of thesupport 22 laminated with the resin film 11, the present invention maybe applied to the case of a resin film 11 alone, namely a resin film notapplied to a support 22. In short, the present invention is applicableto any methods and apparatuses for forming a resin film in whichdifferent kinds of resins are joined.

[0048] The resin A for the middle portion and the resin B for the edgeportions can be joined together in the extruding die 12; however, whenjoining them in the extruding die 12, if the extrusion of the resin filmis carried out at high speed, the film separation becomes likely tooccur, and in addition, the joining part of the extruding die 12 becomeshard to change depending on the condition, such as physical propertiesof the resins and applying condition under which resin films are formed.

EXAMPLE

[0049] In the following, the test results will be described of theexamples with reference to Table 1 in which joining methods according toembodiments of the present invention were used and of ComparativeExamples in which conventional joining methods were used. The resinsused for the tests were as follows.

Comparative Example 1

[0050] A mixture of a melt of low-density polyethylene of 90% by weightwith an MFR of 10 g/10 min and a density of 0.917 g/cm³ and titaniumoxide of 10% by weight, obtained at a resin temperature of 325° C. wasused as a resin A for the middle portion. The same melt of low-densitypolyethylene as above, which had no titanium oxide mixed therein, wasused as a resin B for the edge portion. The resin A for the middleportion and the resin B for the edge portions were joined and layeredtogether in the feed block 13 and extruded through the extruding die 12of 1 meter in width to form a resin film 11. The feed block 13 used wassuch that its joining part 36 was to form a lamination resin 15 in whichthe boundary between the resin A for the middle portion and the resin Bfor the edge portions was a straight line, as shown in FIG. 6.

Example 1

[0051] The same resin A for the middle portion, the same resin B for theedge portion, along with the same extruding die of 1 meter in width asthose of Comparative Example 1 were used. A feed block 13 used was suchthat its joining part 36 was to form a lamination resin 15 by thejoining method according to an embodiment of the present invention inwhich the resin A for the middle portion and the resin B for the edgeportions were joined together in such a manner as to enclose the sideedge portions of the resin film main body 11A, which was formed of theresin A for the middle portion, in the resin B for the edge portion, asshown in FIG. 7.

Comparative Example 2

[0052] A mixture of a melt of low-density polyethylene of 90% by weightwith an MFR of 10 g/10 min and a density of 0.917 g/cm³ and titaniumoxide of 10% by weight, obtained at a resin temperature of 325° C. wasused as a resin A for the middle portion. A melt of low-densitypolyethylene with an MFR of 3 g/10 min and a density of 0.919 g/cm³ wasused as a resin B for the edge portion. A die system in which the resinA for the middle portion and the resin B for the edge portions werejoined at and extruded through an extruding die 12 of 1 meter in widthwas used to form a lamination resin 15 in which the boundary between theresin A for the middle portion and the resin B for the edge portions wasa straight line, as shown in FIG. 6.

Example 2

[0053] The same resin A for the middle portion, the same resin B for theedge portion, along with the same extruding die 12 of 1 meter in widthas those of Comparative Example 2 were used. The resin A for the middleportion and the resin B for the edge portions were joined and layered ina feed block 13 and extruded through the extruding die 12 to form aresin film 11. The feed block 13 used was such that its joining part 36was to form a lamination resin 15 as shown in FIG. 7 by the joiningmethod according to an embodiment of the present invention.

Comparative Example 3

[0054] Two kinds of mixtures of a melt of low-density polyethylene of95% by weight with an MFR of 10 g/10 min and a density of 0.917 g/cm³and titanium oxide of 5% by weight, and the same melt of low-densitypolyethylene of 90% by weight and titanium oxide of 10% by weight,obtained at a resin temperature of 325° C. were used as resins A₁ and A₂for the middle portion. The resins A₁ and A₂ were layered at a thicknessratio of 1:2. A melt of low-density polyethylene with an MFR of 10 g/10min and a density of 0.917 g/cm³ was used as a resin B for the edgeportion. The resins A₁ and A₂ for the middle portion and the resin B forthe edge portions were joined and layered in the feed block 13 andextruded through the extruding die 12 of 1 meter in width to form aresin film 11. The feed block 13 used was such that its joining part 36was to form a lamination resin 15 in which the boundary between theresins A₁ and A₂ for the middle portion and the resin B for the edgeportions was a straight line, as shown in FIG. 8.

Example 3

[0055] The same resins A₁ and A₂ for the middle portion, the same resinB for the edge portion, along with the same extruding die 12 of 1 meterin width as those of Comparative Example 3 were used. The resins A₁ andA₂ for the middle portion and the resin B for the edge portions werejoined and layered in a feed block 13 and extruded through the extrudingdie 12 to form a resin film 11. The feed block 13 used was such that itsjoining part 36 was to form a lamination resin 15 as shown in FIG. 9 bythe joining method according to an embodiment of the present invention.

Example 4

[0056] The same resins A₁ and A₂ for the middle portion, the same resinB for the edge portion, along with the same extruding die 12 of 1 meterin width as those of Comparative Example 3 were used. The resins A₁ andA₂ for the middle portion and the resin B for the edge portions werejoined and layered in a feed block 13 and extruded through the extrudingdie 12 to form a resin film 11. The feed block 13 used was such that itsjoining part 36 was to form a lamination resin 15 by the joining methodaccording to an embodiment of the present invention and in such a manneras to enclose resin A₂ for the middle portion, which contained a largeramount of titanium oxide, with the resin B to a smaller degree and theresin A₁ for the middle portion, which contained a smaller amount oftitanium oxide, in the resin B to a larger degree, as shown in FIG. 10.

Comparative Example 4

[0057] This Comparative Example was carried out under the same conditionas that of Comparative Example 1, except that an extruding die of 2meters in width was used.

Example 5

[0058] The same resin for the middle portion, the same resin for theedge portions, along with the same extruding die as those of ComparativeExample 4 were used. The feed block used was such that its joining partwas to form a resin film in such a manner as to enclose the resin forthe middle portion with the resin for the edge portions to a smallerdegree, as shown in FIG. 11, compared with that shown in FIG. 7. TABLE 1Film Disorder at Width-Direction Die Joining Separation Boundary ResinUsed Layering System Width Configuration of Resins between ResinsComparative A: MFR 10 g/10 min plus Feed block 1 m None Rather Example 1  titanium oxide 10 wt % system observed B: MFR 10 g/10 min Example 1 A:MFR 10 g/10 min plus Feed block ″ None Small   titanium oxide 10 wt %system B: MFR 10 g/10 min Comparative A: MFR 10 g/10 min plus Die system″ Observed Small Example 2   titanium oxide 10 wt % B: MFR 3 g/10 minExample 2 A: MFR 10 g/10 min plus Feed block ″ None Small   titaniumoxide 10 wt % system B: MFR 3 g/10 min Comparative A₁: MFR 10 g/10 minplus Feed block ″ None Large Example 3    titanium oxide 5 wt % systemA₂: MFR 10 g/10 min plus    titanium oxide 10 wt % B: MFR 10 g/10 minExample 3 A₁: MFR 10 g/10 min plus Feed block ″ None Rather    titaniumoxide 5 wt % system observed A₂: MFR 10 g/10 min plus    titanium oxide10 wt % B: MFR 10 g/10 min Example 4 A₁: MFR 10 g/10 min plus Feed block″ None Small    titanium oxide 5 wt % system A₂: MFR 10 g/10 min plus   titanium oxide 10 wt % B: MFR 10 g/10 min Comparative A: MFR 10 g/10 minplus Feed block 2 m None Large Example 4   titanium oxide 10 wt % systemB: MFR 10 g/10 min Example 5 A: MFR 10 g/10 min plus Feed block ″ NoneRather   titanium oxide 10 wt % system observed B: MFR 10 g/10 min

[0059] As seen from the comparison between Comparative Example 1 andExample 1 shown in Table 1, when the boundary between the resin A forthe middle portion and the resin B for the edge portions was made astraight line as in the case of Comparative Example 1, the disorder atthe boundary between the resins was “rather observed”, whereas when thejoining method according to the embodiment of the present invention wasadopted, like the case of Example 1, the disorder at the boundarybetween the resins could be reduced.

[0060] As seen from the comparison between Comparative Example 1 andComparative Example 2, in the case of Comparative Example 2 where thedifference in MFR between the resin A for the middle portion and theresin B for the edge portions was large, the film separation of theresins was more likely to occur, compared with the case of ComparativeExample 1. However, if the joining method according to the embodiment ofthe present invention is adopted, like in the case of Example 2, notonly the film separation can be prevented, but also the disorder at theboundary between the resins can be reduced. Although, the die system wasadopted in Comparative Example 2, even if the feed block system isadopted, the bigger the difference in MFR between the resins becomes,the more the film separation of the resin A for the middle portion andthe resin B for the edge portions is likely to occur.

[0061] Further, as seen from the comparison between Comparative Example1 and Comparative Example 3, in the case of Comparative Example 3 wherethe resin film main body 11A was made up of two layers, the resins A₁and A₂ for the middle portion, the disorder at the boundary between theresins A₁ and A₂ and the resin for the edge portions B was largercompared with the case of Comparative Example 1. However, if the joiningmethod according to the embodiment of the present invention is adopted,like in the case of Example 3, the disorder at the boundary between theresins can be reduced. Moreover like in the case of Example 4, if thejoining method according to the embodiment of the present invention isadopted and, of the two-layered resins A₁ and A₂ for the middle portion,the resin A₂ containing a larger amount of titanium oxide is enclosedwith the resin B for the edge portions to a smaller degree than theresin A₁ containing a smaller amount of titanium oxide, the disorder atthe boundary between the resins can be much more reduced.

[0062] Further, as seen from the comparison between Comparative Example1 and Comparative Example 4, when the width of the resin film 11 wasincreased, from 1 meter in Comparative Example 1 to 2 meters inComparative Example 4 in width of the extruding die, the disorder at theboundary between the resins became large. However, if the joining methodaccording to the embodiment of the present invention is adopted, like inthe case of Example 5, the disorder at the boundary between the resinscan be reduced. In the case of Example 5, the resin A was enclosed withthe resin B to a smaller degree as shown in FIG. 11, compared with thecase shown in FIG. 7.

[0063] These test results proved that adopting the joining methodsaccording to the embodiments of the present invention made it possibleto prevent the film separation of resins and reduce the disorder at theboundary between resins.

[0064] As described so far, according to the method and apparatus offorming a resin film of the present invention, the disorder at theboundary between the resins for the middle portion and for the edgeportion, which constitute the resin film, can be reduced whilepreventing the film separation of the resins. This makes it possible toavoid the inclusion of the resin for the middle portion in the trimmedoff selvages as much as possible, which in turn increases therecyclability of the selvages, and hence the yield and the productivityof the product.

[0065] It should be understood, however, that there is no intention tolimit the invention to the specific forms disclosed, but on thecontrary, the invention is to cover all modifications, alternateconstructions and equivalents falling within the spirit and scope of theinvention as expressed in the appended claims.

What is claimed is:
 1. A method of forming a resin film from a resin fora middle portion to form a resin film main body of the resin film and aresin for edge portions to form both side edge portions in a crosswisedirection of the resin film, the method comprising the steps of: joiningthe resin for the middle portion in a molten state and the resin for theedge portions in a molten state in such a manner as to enclose both sideedges in the crosswise direction of the resin film main body with theresin for the edge portions; and extruding the joined resins through anextruding die to form the resin film.
 2. The method as defined in claim1, wherein a degree of enclosing the resin for the middle portion withthe resin for the edge portions is adjusted according to a difference inMFR between the resins.
 3. The method as defined in claim 1, wherein adegree of enclosing the resin for the middle portion with the resin forthe edge portions is adjusted according to a difference in extrusionrate between the resins.
 4. The method as defined in claim 1, wherein adegree of enclosing the resin for the middle portion with the resin forthe edge portions is adjusted according to a difference in resintemperature between the resins.
 5. The method as defined in claim 1,wherein a degree of enclosing the resin for the middle portion with theresin for the edge portions is adjusted according to a width of theresin film.
 6. An apparatus for forming a resin film from a resin for amiddle portion to form a resin film main body of the resin film and aresin for edge portions to form both side edge portions in a crosswisedirection of the resin film, the apparatus comprising: a feed blockwhich includes a joining part where the resin for the middle portion ina molten state and the resin for the edge portions in a molten state arejoined in such a manner as to enclose both side edges in the crosswisedirection of the resin film main body with the resin for the edgeportions; and an extruding die through which the joined resins areextruded to form the resin film.
 7. The apparatus as defined in claim 6,wherein: a trunk flow path through which the resin for the middleportion flows and a pair of branch flow paths through which the resinfor the edge portions flows are joined at the joining part in the feedblock; and a cross-sectional shape of the joining part is formed toallow the side edges of the resin film main body to be enclosed with theresin for the edge portions.
 8. The apparatus as defined in claim 6,wherein: the feed block is adapted to be detachably provided with anyone of a plurality of joining part blocks having respective joiningparts different in degree of enclosing the side edges of the resin filmmain body with the resin for the edge portions; and one of the pluralityof joining part blocks which specifies a joining configuration dependingon condition under which the resin film is formed is attached to thefeed block exchangeably for another of the plurality of joining partblocks.
 9. The apparatus as defined in claim 8, wherein the conditionunder which the resin film is formed includes at least one of adifference in MFR, an extrusion rate and resin temperature between theresin for the middle portion and the resin for the edge portions and awidth of the resin film.